Hydroxyl radical formation in aqueous reactions (pH 3-8) of iron(II) with hydrogen peroxide: the photo-Fenton reaction

Abstract

Kinetics studies of the indirect photooxidation of trace hydroxyl radical (^̇OH) probes in aqueous solutions were used to evaluate the nature and formation efficiency of the transient oxidants that are generated when hydrogen peroxide reacts with Fe(II) that is produced from photoreduction of Fe(III) (λ = 436 nm). Results of studies of these "photo-Fenton reactions" under various test conditions are in good agreement with the hypothesis that Fe²⁺ and its oxalate, citrate, and phosphate complexes react with H₂O₂ efficiently to produce ^̇OH in water at pH values ranging from 3 to 8. Such reactions involving Fe(II) and H₂O₂ provide a generally important pathway for oxidations in the environment and possibly for the treatment of contaminated waters.